This invention relates generally to irrigation equipment and systems and in particular to equipment for systems employing a plurality of serially arranged stations to which a supply of irrigation water is to be sequentially delivered. The invention is an improvement in the equipment and systems described and claimed in my earlier U.S. Pat. Nos. 3,797,253; 3,951,163; and 4,014,361.
In many orchards, it is required that individual trees be watered by flooding a small basin formed around the base of the tree. In my earlier patents, of which U.S. Pat. No. 3,797,253 is representative, this is effected by providing a valve in each basin and serially connecting the valves to each other and to a source of pressured water. Each valve has a body with an inlet, a primary outlet, a secondary or flow-through outlet; and a float actuated closure member for selectively opening and closing the primary outlet. The inlet and flow-through outlets are connected into a closed conduit by which pressured water is supplied to the system while the primary outlet, when open, communicates directly with the atmosphere and the basin through a relatively large opening. Each valve has a closure member actuated in response to the level of water in the basin so that when sufficient water flows into the basin the primary outlet closes and water is diverted to the next valve in line. The closure member once in place over the primary outlet is adapted to be held there by internal water pressure thereby holding the outlet closed. The system also includes for each valve a delay means to block water from the next valve in line until after the first basin is filled and the primary outlet of the first valve is closed.
In my earlier U.S. Pat. No. 3,797,253 the delay means comprises an inverted vertical U following each valve in the system except possibly the last one. Water entering the riser leg of the inverted U encounters a resistance thus creating a back pressure to force water through the open primary outlet of the preceding valve. This flow continues until the respective basin fills and the float actuated closure member covers and closes the primary outlet. When this closure occurs, the water immediately flows on through the inverted U into the succeeding valve where the cycle is repeated. The sequence continues until all basins are filled and all primary valve outlets closed. In a given valve, once the primary outlet closes it should remain closed so long as there is pressure in the system even though water in a basin may drain completely away and there is no longer support for the floats. This is because only a modest internal pressure in the system is needed to hold the closure member over the primary outlet. After all basins are filled, system pressure is cut off and the basins drain thereby allowing all primary outlets to reopen for the next complete sequencing.
The system as described is operable, however, it is still not all that is to be desired in all situations. For instance, in many cases there may be a chattering of the float actuated closure and, even worse, a premature reopening of a primary valve outlet. These are due to hydraulic phenomena demonstrated in the system at the time whenever one of the primary outlets is closed and there is a sudden upset in the water flow into the next valve and out its primary outlet to atmospheric pressure. In other words, when the primary outlet of a valve is closed by the float actuated member, the closure is very sudden and the resulting flow out the secondary outlet through the conduit to the inlet of the next valve is very abrupt. Indeed it may be likened to a bullet. Then, immediately upon entering the next valve body, which is open to the atmosphere through the primary outlet, there is an almost instantaneous loss of pressure which is transmitted back through the closed conduit to all of the preceding closed system. The result is a loss of pressure in the system thereby temporarily releasing the pressure that holds the closure member against the primary outlet of the preceding valve. In cases where the water around the valve has drained to the point where the above closure means is ineffective, the pressure loss will allow the primary outlet to reopen thereby releasing all pressure downstream from the outlet until the primary outlet is reclosed. (There will also be an annoying chattering and possible damage due to a hunting action as the closure members vibrate between partly open and fully closed position.) The effect of reopening a primary outlet is to interrupt the sequence, thus opening all downstream primary outlets and forcing a repeat of the cycles. Automatic operation is thus thwarted and recourse to manual control is needed to complete the proper irrigation sequence.